We devised a procedure to obtain cloned DNA of influenza viral RNA sequences. Influenza viral gene segments that code for the hemagglutinin (HA), neuraminidase (NA), nucleoprotein (NP), matrix protein (M), non-structural proteins (NS) and one of the three polymerase proteins (Pi) were cloned in pBR322 of E. coli. Results from sequence analysis of several DNA clones provide evidence that cellular RNA sequences are utilized to prime influenza viral mRNA transcription in infected cells. Mapping of mRNA species as probed by the cloned NS DNA showed that two separate NS mRNA's are responsible for the NS1 and the NS2 polypeptides: the NS1 mRNA is a continuous transcript and the NS2 mRNA contains an interruption. Similarly, mapping of M mRNA transcripts revealed the presence of a colinear mRNA and two different interrupted mRNA's. These findings indicate that the M RNA potentially codes for 3 different polypeptides. Also, an HA-SV40 hybrid virus was constructed for expression of functional activity of the hemagglutinin in primate cells. The putative hemagglutinin produced in this system was glycoslyated and exhibited hemagglutination activity. Furthermore, the hemagglutinin product of the hybrid virus was detected on the surface of infected cells.